First Aid & Emergencies

Heat-Related Illnesses - Topic Overview

A healthy body temperature is maintained by
the nervous system. As the body temperature increases, the
body tries to maintain its normal temperature by
transferring heat. Sweating and
blood flow to the skin (thermoregulation) help us keep our
bodies cool. A heat-related illness occurs when our bodies can no longer
transfer enough heat to keep us cool.

A high body temperature
(hyperthermia) can develop rapidly in extremely hot
environments, such as when a child is left in a car in the summer heat. Hot
temperatures can also build up in small spaces where the ventilation is poor,
such as attics or boiler rooms. People working in these environments may
quickly develop hyperthermia.

High temperature caused by a
fever is different from a high body temperature caused
by a heat-related illness. A fever is the body's normal reaction to infection
and other conditions, both minor and serious. Heat-related illnesses produce a
high body temperature because the body cannot transfer heat effectively or
because external heat gain is excessive.

Heat-related illnesses
include:

Heat rash (prickly heat), which occurs when the
sweat ducts to the skin become blocked or swell, causing discomfort and
itching.

Heat cramps, which occur in muscles after exercise
because sweating causes the body to lose water, salt, and minerals (electrolytes).

Heat edema (swelling) in the legs and hands, which can occur when
you sit or stand for a long time in a hot environment.

Heat tetany
(hyperventilation and heat stress), which is usually caused by short periods of
stress in a hot environment.

Heat syncope
(fainting), which occurs from low blood pressure when heat causes the blood
vessels to expand (dilate) and body fluids move into the legs because of
gravity.

Heat exhaustion (heat prostration), which generally
develops when a person is working or exercising in hot weather and does not
drink enough liquids to replace those lost liquids.

Heatstroke (sunstroke), which occurs when the body
fails to regulate its own temperature and body temperature continues to rise,
often to 105°F (40.6°C) or
higher. Heatstroke is a medical emergency. Even with immediate treatment, it can be life-threatening or cause serious long-term problems.